todbeibrot: Of course Black has to start with s5 and t2. Now r1 and o1 should be correct too.
d4rkm4tter: The objective should be to kill without ko. I found only 2 moves that can accomplish it: R1 and N1. I made all correct sequences new and increased the problem difficulty.
Upper left: B15 B16 A18 A17 => E17 C19 G19 considered wrong - why?